扬子西缘羊场磷矿地球化学特征及其对成磷环境的指示  

Geochemical characteristics of the Yangchang phosphate deposit in western margin of the Yangtze Block and its indications of the phosphorus-forming environment

作　　者：周骞 米云川 赵勇 黄太平 王加昇[1] 胡清华 夏建峰 宰西 ZHOU Qian;MI Yun-chuan;ZHAO Yong;HUANG Tai-ping;WANG Jia-sheng;HU Qing-hua;XIA Jian-feng;ZAI Xi(Faculty of Land Resource Engineering,Kunming University of Science and Technology,Kunming 650093,China;Yunnan Institute of Geological Survey(Yunnan Institute of Geological Sciences),Kunming 650216,China;Key Laboratory of Sanjiang Metallogeny and Resources Exploration and Utilization,Ministry of Natural Resources,Kunming 650051,China;Yunnan Key Laboratory of Sanjiang Metallogeny and Resources Exploration and Utilization,Kunming 650051,China;Yunnan Geological Survey,Kunming 650051,China)

机构地区：[1]昆明理工大学国土资源工程学院,云南昆明650093 [2]云南省地质调查院(云南省地质科学研究院),云南昆明650216 [3]自然资源部三江成矿作用及资源勘查利用重点实验室,云南昆明650051 [4]云南省三江成矿作用及资源勘查利用重点实验室,云南昆明650051 [5]云南省地质调查局,云南昆明650051

出　　处：《岩石矿物学杂志》2024年第5期1119-1138,共20页Acta Petrologica et Mineralogica

基　　金：云南省地质勘查基金项目(D202001,K202101,K202301,Y202301)。

摘　　要：寒武纪生命大爆发与海水氧化还原条件息息相关,上扬子地区下寒武统磷块岩较完整记录了早寒武世古海洋环境信息。扬子西缘羊场磷矿床是赋存于下寒武统梅树村组的超大型磷矿床,可重建该时期古海洋环境。本文采用ICP-MS等手段,分析羊场磷矿床磷块岩及其围岩的元素地球化学组成特征,探讨其形成时的环境条件。结果表明,羊场磷矿床磷块岩CIA值为46.40~65.60,平均57.43,显示其风化程度较低,稀土元素总量ΣREE相对较低(140.0×10^(-6)~237.4×10^(-6)),但较富集Y(87.0×10^(-6)~183.2×10^(-6));北美页岩标准化的稀土元素配分模式曲线相对平缓,LREE/HREE值为4.22~7.50,显示出轻重稀土元素分异不明显,具有明显的Ce负异常(δCe=0.22~0.42),Eu异常不明显(δEu=0.90~1.21),U/Th值为2.55~27.68,反映了磷块岩成矿过程中受到热水活动的影响;结合δCe、V/Cr、Y/Ho、Sr/Cu等元素分析认为,由底部震旦纪灯影组,到含磷层寒武纪梅树村组,直至上覆牛蹄塘组,古海洋氧化还原环境由底部的相对还原环境,向上变为氧化环境,直至顶部变为相对还原环境。古气候环境表现为寒冷干燥-温暖湿润交替出现的变化规律,古海水盐度表现为由咸水→半咸水→咸水→淡水的演化过程。综合分析后认为,羊场磷矿床磷块岩形成于相对氧化的咸水和较为干旱的古气候环境,并有热水活动参与成矿。The Cambrian life explosion is closely related to the redox environment of plaeoocean,and the Lower Cam-brian phosphorite in the Upper Yangtze Block has recorded a relatively complete information of the Early Cambrian.The Yangchang phosphate deposit in western margin of the Yangtze Block is a super-large phosphate deposit occur-ring in the Meishucun Formation of the Lower Cambrian,which can reconstruct the paleomarine environment of this period.In this paper,ICP-MS and other techniques were used to analyze the elemental geochemical composition characteristics of the phosphorite and its surrounding rocks and explore the geological environment of the Yangchang phosphate deposit.The results show that the CIA value of phosphorite is 46.40~65.60,with an average of 57.43,indicating that the weathering degree is low,the total amount of rare earth element(ΣREE)in phosphorites in this deposit is relatively low(140.0×10^(-6)~237.4×10^(-6)),but yttrium is relatively rich(87.0×10^(-6)~183.2×10^(-6)).The North American standardized rare earth distribution pattern is relatively flat,the LREE/HREE is of 4.22~7.50,shows that the diffrernce of light and heavy rare earth elements is not obvious,with obvious Ce negative anomaly(0.22~0.42),Eu anomaly is not obvious withδEu of 0.90~1.21,and U/Th ratio of 2.55~27.68,which reflect that the phosphorite was affected by a certain influx of hydrothermal fluid during the sedimentary of phos-phorites.Combined with the analysis ofδCe,V/Cr,Y/Ho,Sr/Cu and other elements,it is indicate that from the bottom of Dengying Formation in the Sinian Period,to the phosphate-bearing layer Cambrian Meishucun Formation,to the upper cover Niutitang Formation,the ancient ocean redox environment changes from the relative reduction environment at the bottom to the oxidation environment upward until the top becomes the relative reduction environ-ment.The paleoclimatic environment is cold and dry-warm and moist alternatively appear.The salinity of ancient seawater is the evolution process of salt water to

关 键 词：磷块岩 梅树村组 沉积环境 羊场磷矿床 扬子地块西缘 

分 类 号：P619.213[天文地球—矿床学] P595[天文地球—地质学]